1. Field of the Invention
The invention relates to a modulation device for use in a charged particle multi-beamlet lithography system. The invention further relates to a charged-particle multi-beamlet lithography system. Finally, the invention relates to a method of modulating charged particle beamlets in a charged-particle multi-beamlet lithography system for transferring a pattern to a target surface.
2. Description of the Related Art
Charged particle multi-beamlet systems are known in the art, for example from U.S. Pat. No. 6,958,804 in the name of the applicant. Such lithography system uses a plurality of charged particle beamlets to transfer a pattern to a target surface. The system may operate with a continuous radiation source or with a source operating at constant frequency. Pattern data are sent to a modulation device arranged to modulate the beamlets by electrostatic deflection. The modulated beamlets are then transferred to the target surface. Generally, during this transfer the diameter of the individual beamlets is reduced. Furthermore, the position of the beamlets with respect to the target surface changes over time, for example due to electrostatic scanning of beamlets and/or movement of the target surface relative to the optical column through which the beamlets are transferred with respect to each other. For example, such relative movement may be established by mechanical movement using a stage provided with a support structure for holding the target. In order to enable a high speed transfer of the pattern to the target surface, optical transmission of pattern data from the control unit to the modulators may be used, for example by using light beams. The modulation device may then include light sensitive elements capable of converting received light signals into corresponding electric signals.
Patterning with a system as described above may suffer from inconsistent pattern transfer due to perturbated modulation of the beamlets. Experiments have shown that the extent of such perturbation is highly unpredictable. As a result, pattern transfer onto a target surface using such system is less reliable than desired.